The Lymphatic System
The Body's Fluid Drainage System - Explained

Lymphatic System

Contents

• What Is The Lymphatic System?
• How It Works
• Structure Of Lymphatic System
• What Other Systems Does It Work With?
• How Does Lymph Move?
• What Is the Connection Between Blood And Lymph?
• Diseases And Disorders
• Summary

Related Diagrams
• The Female Body
• The Human Body Diagram

What Is The Lymphatic System?

The lymphatic system is a network of tubes (capillaries and vessels) that drain excess fluids from the body's cells and return them to the bloodstream for eventual filtering and excretion. An easy way to picture the lymphatic system is to think of the water drainage system in a house: the pipes in your home drain water from the toilet, sink and bath and return it to the main pipe network outside your house for elimination by your local town sewage system. The pipes in your home are the lymphatic system, the main network is your bloodstream and the local town sewage system is your kidneys. If there is a problem with the lymph system it may result in edema (swelling) if excess fluid builds up. The lymph system also plays a major role in protecting the body against infections and cancer. For this reason it is part of the immune system. Additionally, the lymphatic system also plays a part in the absorption of fats from the intestines.

Fluid Drainage: How It Works

In order to understand the lymphatic system you need to understand what happens in the blood circulation system at tissue level. Blood travels to and from tissues throughout the body delivering nutrients and removing waste. Whole blood never leaves the capillaries (tiny blood vessels) but leucocytes and the 'passengers' (oxygen, food and water) can. Once outside the capillaries they are carried by a derivative of blood plasma called tissue fluid (or interstitial fluid). This fluid circulates throughout the tissues, delivering food, oxygen and water to the cells and collecting carbon dioxide and other waste. However, when it has finished its work and needs to return to the blood capillaries, not all of it can pass back through the capillary walls because the pressure inside the capillaries is too high. The fluid that is left is picked up by a different set of capillaries, called the lymphatic capillaries.

Lymphatic capillaries have larger pores in their walls than blood capillaries and the pressure inside them is lower. Thus, excess tissue fluid, substances made of large molecules, fragments of damaged cells and foreign matter such as micro-organisms drain away into them. The fluid, known as lymph, is filtered by the lymph nodes then collected by the lymphatic ducts before entering the right and left subclavian veins and returning to the bloodstream. At any one time an average of 1 to 2 liters of lymph fluid is circulating the body.

Structure Of Lymphatic System

The lymphatic system consists of:

1. Lymphatic capillaries
2. Lymphatic vessels
3. Lymph nodes
4. Lymphatic ducts
5. The fluid in lymphatic capillaries and vessels is called lymph.
6. Organs such as the spleen, thymus, tonsils and adenoids contain lymphatic tissue and are part of the overall system.

Lymphatic Capillaries

Description: The vessels which work with blood to collect excess tissue fluid. Lymphatic capillaries eventually unite to form lymphatic vessels.
Structure: Fine, permeable tubes, composed of a single layer of endothelial cells. They occur in all spaces between tissues, except in the central nervous system.
Function: Carry excess tissue fluid away from tissues.

Lymphatic Vessels

Description: These are vessels which transport lymph around the lymphatic system.
Structure: Thin-walled, collapsible vessels similar to veins but carrying lymph not venous blood. They have valves (semi-lunar) to keep the lymph moving centripetally (in the direction of the heart) and prevent back flow. Consisting of a double layer of lining membrane, these valves give the vessels a knotted or beaded appearance. They have three layers:
• an outer layer of fibrous tissue
• a middle layer of muscular and elastic tissue
• an inner layer of endothelial cells.
Function: Lymphatic vessels collect lymph from the lymphatic capillaries and then convey lymph towards the heart. Many lymph vessels run into the subcutaneous tissue (beneath the dermis, see skin structure) and all the lymphatic vessels pass through one or more lymphatic nodes.

Lymph Nodes (Lymph Glands)

Description: All the small and medium-sized lymph vessels open into lymph nodes, which are strategically placed throughout the body. An afferent vessel transports lymph to the node and an efferent vessel transports the filtered lymph back to the system.

Structure: Each node is made of lymphatic tissue, surrounded by a wall of tough, white fibrous tissue supported by inward strands of fibrous tissue called trabecule. Lymph nodes vary in size.
Functions:
• To filter the lymph, remove and destroy harmful micro-organisms, cancer tumor cells, damaged or dead tissue cells, large protein molecules and toxic substances. This filtering system prevents toxic materials from reaching the bloodstream and causing septicemia. If this occurs, it can cause the node to swell. In severe cases, this may cause cell destruction and an abscess on the node.
• To produce new lymphocytes and antibodies and add them to the lymph as necessary.
• Lymphatic tissue cells within the node may become activated to form antibodies against a particular infection. They may then continue to form antibodies for several years or even a lifetime.

Lymphatic Tissue
Description: Lymph nodes are made of lymphatic tissue. This contains many types of cells:
• phagocytes-white blood cells that engulf and destroy harmful (pathogenic) waste and bacteria
• lymphocytes - white blood cells that produce antibodies
• cells dividing to form new lymphocytes.

Special areas of the body containing lymphatic tissue:
• Tonsils
• Thymus gland (behind sternum)
• Peyer's patches (wall of small intestine)
• Appendix
• Spleen

Lymphatic Ducts

All lymph passes into two main lymphatic vessels, or ducts:
1. The right lymphatic duct
This is only 1.5cm long, positioned at the root of the neck and empties into the right subclavian vein to rejoin the circulatory system.
Function: receives all the drained lymph from the right side of the head, chest and neck and from the right arm.
2. The thoracic duct
This is the largest lymphatic vessel. It is 40cm long extending from the second lumbar vertebra to the root of the neck and empties into the subclavian vein to rejoin the circulatory system.
Function: collects and drains lymph from the left side of the head, the neck, both lower limbs, the left side of the trunk and the left arm.

Spleen

Description: The spleen is an organ which both produces and destroys cells. It is a nonessential organ and is sometimes removed due to damage after accidents, as other organs can perform the same functions. The spleen lies on the upper left-hand side of the abdomen.
Structure: The spleen has an outer capsule of fibrous tissue extending into a network of fibrous strands called trabeculae. This network supports the splenic pulp which consists of several different types of cells.
Functions:
• forms new lymphocytes
• destroys thrombocytes and erythrocytes
• helps to remove foreign particles from the circulation
• helps to fight infection, becoming enlarged in certain diseases, e.g. malaria and typhoid fever
• acts as a blood reservoir. Blood sinuses within the spleen normally hold a large amount of blood which is pushed into general circulation if the spleen contracts. Contraction usually occurs two or three times a minute, but in cases of shock or even during exercise, the spleen may contract faster and for a longer period to help maintain pressure in the circulation.

Interrelationships: What Other Systems Does It Work With?

The lymphatic system links to:

Circulatory System: The lymphatic system transports excess waste and toxins that the circulatory system cannot cope with, away from the cells and tissues. It also works closely with the circulatory system to strengthen the body's immunity.

Digestive System: Lymphatic vessels in the small intestines (inside the lacteal of the ileum) help with the absorption of fats during digestion. These are then transported around the body in the circulatory system and distributed to cells to be used as energy.

Muscular System: Lactic acid formed when over-exercising muscles, or from tension and general fatigue in the muscular system, is drained away in the lymphatic system.

How Does Lymph Move?

The lymphatic system has no pump to make the lymph fluid move. Instead fluid is circulated as a side effect of muscle movement (physical activity) and heartbeats. When the muscles in our body contract they squeeze (compress) the lymph vessels so that lymph fluid is moved on. Valves inside the vessels (which only open in one direction) ensure that the fluid always flows in the right direction.

What Is the Connection Between Blood And Lymph?

The lymphatic system is a subsidiary circulation, helping the blood circulation to carry out its functions. It removes excess fluid from tissues and carries large particles that cannot pass through the smaller pores of the blood capillaries. Lymph nodes and the spleen filter lymph (the name of the fluid in the lymphatic system) and take out the waste materials it contains as well as producing antibodies and lymphocytes which are added to the lymph to be transported to the blood.

Diseases And Disorders (Pathologies)

When you have an infection (such as a cold), the lymph nodes (sometime referred to as 'glands') in your neck or groin or under your arm may swell. This is a sign that white blood cells (lymphocytes) are fighting germs. If the infection is severe, the vessels leading from the nodes can become inflamed (lymphangitis). The following is a list of other common, and less common diseases and disorders that affect the lymph system:

Edema/water retention: Temporary swelling due to excess fluid in the body’s tissues. Typically affects the legs, ankles, feet and hands but can involve your whole body. Water pills (diuretics) can help your body excrete fluids.

Lymphedema: Chronic long-term edema which may result from cancer surgery, radiotherapy, trauma, allergic reaction, lack of movement or parasites (worms blocking a lymphatic vessel).

Hodgkin's disease: Cancer of the lymphatic tissue.

Cancer: The fastest way for cancer to spread throughout the body is via the lymphatic system. If a cancer tumor (lump) invades a nearby lymph vessel, cancer cells from the tumor can break off and enter the vessel (known as metastasis). They may become lodged in nearby lymph nodes when they grow into a secondary tumor. For example, with breast cancer, cells from the breast lump can spread to the lymph nodes in the armpit. In advanced stages, cancer cells travel through the lymph to other parts of the body. See stages of breast cancer.

Cellulite: Lumpy deposits of body fat (described as orange-peel appearance) especially on women's thighs. See, what is the best treatment for cellulite?

Infectious mononucleosis (glandular fever): A viral infection caused by the Epstein-Barr virus. It causes swollen lymph nodes (usually the neck), a sore throat and extreme tiredness. Those between the ages of 10 and 25 are most prone to infection. The illness usually passes without serious problems. It’s not highly contagious. The virus can be transported via air droplets or transmitted by kissing.

Lymphadenitis: The inflammation of lymph nodes.

Non-Hodgkin lymphoma: A type of lymphoma, a cancer in the lymphatic system; causes the cells in the lymphatic system to abnormally reproduce, eventually causing tumors to grow.

Hashimoto's thyroiditis (chronic lymphocytic thyroiditis): A type of thyroid disease. Hashimoto's is an autoimmune disease where the body's own T-cells attack the cells of the thyroid.

Lymphoma: Is a type of cancer that originates in lymphocytes of the immune system. They often first form in lymph nodes where they cause a tumor to grow (presenting as an enlargement of the node).

Systemic lupus erythematosus (SLE) or just lupus: Lupus is an autoimmune disease that affects connective tissues in the body (including the skin, joints, brain, kidneys). Symptoms include fever, weakness, joint pains and skin rash on the face, neck or arms (characteristic butterfly rash across the nose).

SUMMARY Of Lymphatic System

• Provides a channel for transporting excess tissue fluid away from tissues and back to the blood circulation.
• Collects and transports lymph from tissue cells.
• Nodes (glands) filter lymph of harmful materials before returning it to the blood circulation. Produces new lymphocytes (white blood cells).
• Produces antibodies.
• Lymphatic capillaries in the lining of the small intestine assist in the absorption of fat droplets.

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